This invention relates generally to rotational viscometers and more particularly to rotational viscometers designed for use with fluids at high temperatures and pressures.
The invention was developed to provide a relatively simple and inexpensive instrument for monitoring viscosity and/or viscosity changes in high-temperature, high-pressure liquid streams, such as those encountered in coal-liquefaction processes. Such streams may have temperatures on the order of 900.degree. F. and pressures of 3,000 psi or even higher. Furthermore, the streams may be highly corrosive. Conventional rotational viscometers are not well suited for operation under such severe conditions. Conventional continuous-capillary viscometer systems have been utilized in such applications but are bulky, complex, and expensive. Various conventional viscometers are described in the following publications: Instrument Engineers' Handbook, Vol. 1, "Process Measurement," B. G. Liptak, Chilton, Philadelphia (1969); Viscosity and Flow Measurement, Van Wazer et al, Interscience Publishers (1963).